Drilling fluids used in wells being drilled serve many purposes. The hydrostatic pressure produced by the column of drilling fluid helps contain downhole pressures produced when the earth overburden is drilled away to make a hole, or well. The drilling fluid is circulated downhole, usually through the drill string bore, to rise in the well outside the drill string to lift cuttings produced by the drill head, to the earth surface.
Secondary purposes served by the drilling fluid include scavenging of cuttings from the hole face with fluid velocity produced by nozzles in the drill head, or bit. Additionally, drilling fluids reduce formation porosity and even occlude small fractures to reduce the loss of drilling fluids into formations. There are other functions of drilling fluid, including chemicals and lubricants, to enhance drilling and hole wall conditioning.
High velocity fluid jets ejected through bit nozzles very near the hole face have a useless and negative side effect. The velocity energy is converted to static pressure at the hole face.
Total fluid pressure, or effective hydrostatic pressure, at the drilling face includes hydrostatic pressure produced by a column of drilling fluid standing in the well plus that pressure resulting from impingement of drilling fluid ejected from nozzles in the drill head against the drilling face. Fluid pressure at the drilling face is known, in many cases, to reduce drilling penetration rate. Reducing overall hydrostatic head to increase penetration rate invites well blowouts and is seldom an acceptable practice. Reducing fluid jet velocity to reduce the pressure on the hole face sacrifices scouring ability and usually results in cutting regrinding by the bit with a resulting net loss in penetration rate.
Attempts have been made to use upwardly directed fluid jets near the drill head, in addition to the downwardly directed jets in the drill head, to reduce effective hydrostatic pressure on the well drilling face. This has experienced some beneficial effects, but in most drilling situations, there is not enough fluid power downhole to adequately serve all jets.
This invention is directed to the provision of a fluid pulser valve near the bit to give brief reductions of fluid flow to the drill head jets followed by a brief increase in flow to scour the hole face. Brief reduction of jet velocity harmlessly reduces effective hydrostatic pressure at the hole face and benefits penetration. The interval of brief fluid flow reduction stores energy in the fluid supply system due to elasticity of all materials involved, and the subsequent direction of stored hydraulic energy through the opening pulser valve and through the drill head nozzles helps to thoroughly scour the hole face of cuttings.
It is therefore an object of this invention to provide a pulser valve in a drilling fluid system in a drill string, near the drill head, to improve penetration rate.
It is another object of this invention to provide apparatus to direct the principal flow of drilling fluid alternately to drill head fluid channels and to bypass channels.
It is yet another object of this invention to provide apparatus to briefly and periodically impede the flow of drilling fluid through drill head fluid channels and to provide drilling fluid bypass channels upstream of the means to impede flow.
It is still another object of this invention to provide apparatus to generate pulsations in the flow of fluid to drill head fluid channels and to provide a free running pulse generator valve that requires no external controls.
It is still a further object of this invention to provide drilling enhancement fluid flow pulser apparatus that permits back flow of fluid to fill the related drill string bore, with valve equipment that will close in response to high rates of forward flow of drilling fluid.
It is yet another object of this invention to provide means to avoid excessive oscillation amplitude in unstable pulse generating elements of a drilling enhancement drilling fluid flow pulser.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached drawings and appended claims.